1000000030

H Y D

imrerr~t\ly,

as in the ehaleedoryy ; and giving a gene–

r.i1 clouuinefs or millinefs to thc 1I0nc, but al" fo im–

perfeét and irregul, r an admixtu re, as not to be e' pa–

ble of fa good apoli/h as the ehalecdony; and appear–

ing of a dufl¡y anu foul furfaee, tiU thrown imo water,

in ",hich they beeollle lucid, and in fome degrec tranf–

parent, either in p.\ft or

tot~Uy ;

alfo ehanging their

colour. wh ieh relurns lO themon being taken out of

the water.

To Ibis

~en\ls

belong the oeulus beli of authors, or

whitifh -grey hydroph,mes, variega1ed with y. Uuw, ¡nd

with 'a blaek central nucleus ; and the oeulus mundi,

or lapis muubilis, whieh is Iikewife a whilifh-grey kind

without veios.

HYDROPHOBIA, an

av~rfion

or drcad of water

H Y D

terrible {ymptom of the rabiel eaoina. See MEDICIMI,

OIWPti

LLUM, In butany, a genu. of tbe pentaD–

dáa

mo~ogynia

claf,. The carolla

bell-fh.ped ; the

f1'gma IS bifid; and the eapfule is roundifh wilh t"'O

valves. Thcre are two fpecie" nooe of thero oalives

of Britaio.

HYDROPS, in medieioe, SeeMEDteINI.

HYDROSeOPE, an inllrument anciently ufed for !he

/lleafuring of time.

. The hydrofcope wal a kind of water·dock,

eonr.rl–

Ing of a eylindrieal tub, conical at bonom : the eylin–

der was graduated, or marked OUt with divir.ons, tO

whieh the' top of the water becoming fuccellively con–

tiguo"s, as it tricJded out at the verte" of tbe CODe,

poioteu out tbe bour,

H Y D R O S T A

TIC

feieoeeof

YD~OSTA

es treats of the oature

gravit y, prelfure, aod motioo of fluids in geDeral ;

.nd of weighiog folids in them.

A fluid is a body that yields to the leall prelfure or

difference of prelfures. !ts partid es are fa exeeedingly

fmall, that lhey eannot be difeerned by thebe(l of micro–

(,opes; lhey are hard, fi oee no fluid, exeepl air or Ileam,

can be prelfed ioto a lefs fpaee lhan il naluraUypolfelfes ;

and they are

roun~

and fmoolh,

fioe~

they are fa eafily

moved among one another.

AII bodies, bOlh fluid and folid, prefs downwards by

the force of gravity: but flu ids have this wonderful pro

perty, that their prelfure upwards and fidewife is equal

to their prelfure downwards; and lhis is always in pro.

portion to lheir perpendicular heighl, wilhout any re–

~ard

tO their quantilY: for, as eaeh partide is quile free

to move, it will move towards lhat pan or

r.de

whieh lhe prelfure is leafl. And henee, no particle or

quaolily of a fluid can be al rell, till il is every way e-

4jually prtlred.

(Plate XCIX. fig. 2.) To fhew by experiment lhat

Iluids prefs up",ard as well as dowqward, let AB be a

long upright lube filled wilh IValer oear to ilS top ; and

CD a fmall tube 9pen at bOlh eods, and immerfed inlo

tbe waler in Ihe large one: if lhe immerfion be qUlCk,

yon will fce Ihe wate,r rife in the fmall tube to rhe

fa.me

heighl that il (Iands In the great one, or Unltllhe lur

{aees of lhe water in bOlh are on the fame level : whieh

fhew! lhal the waler is

prelf~d

upward into lhe fmall tube

by the weigh'l of

Wh~l

is in the

grea~

ooe;

olherwi~e

cou!d never rife therem, conlrary lO lIS oatUr I eravuy ;

unlefs the

~iameter

of Ihe bore were fo fntall, Ihal lhe

amaétion of ¡he tube would raife the waler; whiell will

neva h.ppen, if the tube be as wide as Ihat in a eommon

haromeler. Ano as lhe waler rifes no Itigher in Ihe

fmall hlbe lhan lill ils furf,ee be on a lev(·1 ilh lhe fur

{ace of the waler in lhe great

one,

lhis fhews that lhe

r rclfure is nOl io proportion to.Ilte

qu~ntity

of IVa.ter in

the ¡:reat

lub~,

but

proporlton lO

liS

perpendlcul. r

heighl therein: for there is mleh more water in the

great tube all around the finall ooe, thao wnat is rai–

fed to lhe fame height in the {mall ooe, as it (Iaads in lhe

great.

Take out lhe

fma.ll

tube, and let ihe water rIIn OUI of

it; then it will be filled wilh airo Stop itl upper end

with lhe eork e, and it will be full of air all be/ow the

eork: this dooe, plunge it again to the bOllOmof the

water io Ihe great tube, aoJ you wiUfee the water rife

up io it

the height E ; whieh /hews lhat Ihe air is

body, olherwife it eould not hinder lhe wm r

fromrir.ng

Ihe fa me height as it did before, name/y,

and in fo

doi~g

il drove the air out at the tOP; but nOIf

the air is eonfioed by the eork e: aod it alfo fhe "'.

that lhe air is a eomprellible body; for if it were no!

fo, a drop of water could oot eoter inlo the tube.

'fhe prelfure of fluids being equal in all di reétions, it

rollows, that the fides of a velfel are as mlleh prelfed by

fl uid in it, all around inany giveo ring of poi nls, as lhe

fl uid betow Ihat ring is prelfed by the weighl of al! Ihal

Ilands above il. Henee lhe prelfure upon every poinl in

lhe fides, immediately above lhe bOllom, is equal to the

prelfure upon every poiol of lh'e bOllom. To fhew this

by experimeot, let a hale be made at E (fig 3.) in the

fide of lhe lube AS cJofe by lhe boltom; and another

hole of the fame

r.ze

in lhe boltom, al C; then pour

water into lhe tube, keeping it fuI! as long asyou chufe

Ihe holes /hould run, and have tlVO tWO bafons ready

reeeive Ihe water lhat runs through Ihe two holes, until

you think there is enough in eaeh bafon; and you will

find , hy meafuring'the quainlilies. lh.l they He equ,l ;

whieh /hews that

th~

wmr ruo wilh equal freed throuch

bOl': holes: whieh it eould nOl have done, ir il

h~d

not

bl'en equally prelfrd throllgh Ihem both: for if • hole

of Ihe fame h ebe madein the

r.de

of Ihe tube. as

,bOlIlI

and if all lhree art permilled

rIln

togl·lh~r.

y"u .,11

fino that Ihe quanlily IIIn through lhe hole al

r i~ mll,~

Ids

Ihan ..hal has runin Ihe fame

tiUl~ lb(~lIgh

eilha of

lhe hules C or

l .